Method of operating a heat pump

ABSTRACT

A method of operating a heat pump having an inside heat exchanger, an outside heat exchanger, a compressor, and valves that control the circulation of a refrigerant such that in one operating mode the inside heat exchanger operates as an evaporator while in the other operating mode it operates as a condenser. When switching from one operating mode to the other operating mode first the compressor is stopped, then the inside heat exchanger and the outside heat exchanger are directly connected via the valves until pressure is equal in both of the heat exchangers. Subsequently the valves are moved back into the positions appropriate for the desired operating mode, and the compressor is restarted.

FIELD OF THE INVENTION

The present invention relates to a heating-cooling system. Moreparticularly this invention concerns a method operating a heat pump.

BACKGROUND OF THE INVENTION

A typical heat pump for operation as a building's heating and coolingsystem has an inside heat exchanger and an outside heat exchanger aswell as a compressor and valves that control the circulation of arefrigerant such that in one operating mode the inside heat exchangeroperates as an evaporator while in the other operating mode it operatesas a condenser.

Compressors in air conditioners and heat pumps can compress only gaseousrefrigerants; they break down if they draw in liquid. In order toprotect the compressor, a liquid separator is integrated into thecooling circuit in known equipment so as to ensure that no liquidcomponents are drawn in by the compressor. The requisite inclusion of aliquid separator makes the known units more expensive and also requirescostly construction.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide animproved method of operating a heat pump.

Another object is the provision of such an improved method of operatinga heat pump that overcomes the above-given disadvantages, in particularthat renders a liquid separator unnecessary.

SUMMARY OF THE INVENTION

A method of operating a heat pump having an inside heat exchanger, anoutside heat exchanger, a compressor, and valves that control thecirculation of a refrigerant such that in one operating mode the insideheat exchanger operates as an evaporator while in the other operatingmode it operates as a condenser. When switching from one operating modeto the other operating mode first the compressor is stopped, then theinside heat exchanger and the outside heat exchanger are directlyconnected via the valves until pressure is equal in both of the heatexchangers. Subsequently the valves are moved back into the positionsappropriate for the desired operating mode, and the compressor isrestarted.

In other words, with this invention there is an equalization of pressureduring the switch in operating modes. This ensures that, withappropriate dimensioning of the system, all the refrigerant is vaporizedand there is no liquid that could get sucked into and damage thecompressor

In the system of this invention two valves are connected upstream of thecompressor while two valves are connected downstream of the compressor.Thus, depending on the operating mode, one of the valves can be switchedover to the outside heat exchanger while the other can be switched overto the inside heat exchanger.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a schematic diagram of a heat pump according to the inventionwhen operating as an air conditioner for cooling;

FIG. 2 is a schematic diagram of the heat pump when operating diagram ofa unit according to the invention when operating as a heater;

FIG. 3 is the circuit diagram of a unit according to the inventionundergoing pressure equalization.

SPECIFIC DESCRIPTION OF THE INVENTION

In the drawing, the gaseous state of the refrigerant is indicated bydots while the liquid state of the refrigerant is indicated by wavywaves in the outside and inside heat exchangers. The heat pump hassolenoid flow-control (on-off) valves 1-6, expansion valves 7 and 8 withbuilt-in check valves, a storage tank 9, the outside heat exchanger, theinside heat exchanger, and a compressor 12.

In the cooling mode of FIG. 1, the valves 1, 3 and 5 are held open bytheir solenoids. The valves 2, 4 and 6 are closed. The compressor 12compresses gaseous refrigerant that flows under high pressure throughthe solenoid valve 1 to the outside heat exchanger 10.

The refrigerant releases its heat to the ambient air in the outside heatexchanger 10 and is thus liquefied. The outside heat exchanger in thisoperating mode is a condenser.

While a liquid and under high pressure, the refrigerant then flowsthrough the tank 9 and via the solenoid valve 5 to the expansion valve7. This expansion valve 7 abruptly lowers the refrigerant's pressure toadiabatically cool it while simultaneously converting it back intovapor. In the inside heat exchanger 11 the refrigerant absorbs heat fromthe ambient air until the refrigerant is completely converted to vapor.The inside heat exchanger in this operating mode is an evaporator.

The now once again gaseous refrigerant is drawn in by the compressor 12via the solenoid valve 3 and again compressed. The cycle starts again.

In the heating mode, the valves 2, 4 and 6 are held open by theirsolenoids. The valves 1, 3 and 5 are closed. The compressor 12compresses the gaseous refrigerant that now flows under high pressurevia solenoid valve 4 to the inside heat exchanger 11.

In this inside heat exchanger 11 the refrigerant releases its heat tothe ambient air and is thereby liquefied. The inside heat exchanger inthis operating mode is a condenser.

As a high-pressure liquid, the refrigerant flows through the tank 9 viathe solenoid valve 6 to the expansion valve 8 that abruptly lowers therefrigerant's pressure, which not only results cooling the refrigerant,but also converts it back to vapor.

In the outside heat exchanger 10 the partly vaporized refrigerantabsorbs heat from the ambient air until it has vaporized. The outsideheat exchanger in this operating mode is an evaporator.

The now once again gaseous refrigerant is drawn in by the compressor 12via the solenoid valve 2 and is again compressed. The cycle starts againfrom the beginning.

The compressor 12 always takes in only gaseous refrigerant from therespective evaporator both in the heating mode as well as in the coolingmode. The functions of heat exchangers 10 and 11 change when theoperating modes are switched in that the evaporator becomes thecondenser and vice versa. The problem in switching operating modesresults from the fact that, after the switch, the compressor 12 isdrawing in from whichever heat exchanger 10 and 11 was previously stilloperating as a condenser. A certain portion of liquid refrigerant isalways in the condenser and would destroy the compressor 12 if it wereto reach the compressor. It is critical to ensure that no liquidcomponents from the heat exchanger are drawn in simultaneously.

Thus the instant invention proposes an equalization of pressure duringthe switch in operating modes. First the compressor 12 is stopped andall the solenoid valves 1-6 are closed.

Subsequently the outside heat exchanger 10 and inside heat exchanger 11are directly connected to each other. This occurs by opening only thesolenoid valves 2 and 3. The result is equalization of pressure andtemperature between the hot condenser that was previously under highpressure and the cold evaporator that is under low pressure. Thecomponents and tubing of the unit must be sized in such a way that therefrigerant after complete equalization is at a temperature-pressurelevel in which it is in a completely gaseous state.

Once this state has been reached, the valves 2 and 3 are closed again.Then for cooling the valves 1, 3, and 5 are reopened. For heating valves2, 4, 6 are reopened.

Finally the compressor 12 is started.

The term “valves” used above must not be understood in a narrow meaning.Instead the term is meant to comprise all shutoff elements that servethe desired purpose. Control of the “valves” is effected based on therequirements of the apparatus-internal control unit arising according tothe invention.

I claim:
 1. A method of operating a heat pump having: an inside heatexchanger; an outside heat exchanger; a compressor; and valves thatcontrol the circulation of a refrigerant such that in one operating modethe inside heat exchanger operates as an evaporator while in the otheroperating mode it operates as a condenser, the method comprising thesteps when switching from one operating mode to the other operating modeof sequentially: stopping the compressor; directly connecting the insideheat exchanger and the outside heat exchanger via the valves untilpressure is equal in both of the heat exchangers; moving the valves intothe positions appropriate for the desired operating mode; and restartingthe compressor.
 2. The method defined in claim 1, wherein the valvesinclude: a first valve connected between an output of the compressor andthe outside heat exchanger; a second valve connected between the intakeof the compressor and the inside heat exchanger; a third valve connectedbetween the intake of the compressor and the inside heat exchanger; anda fourth valve connected between the output of the compressor and theinside heat exchanger.
 3. The method defined in claim 1, wherein in acooling mode the first and third valves are open and the second andfourth valves are closed; in a heating mode the first and third valvesare closed and the second and fourth valves are open; and the inside andoutside heat exchanges are directly connected for pressure equalizationby opening the first through fourth valves.